FEA for Machinery and Robotics: 8 Analyses for Stiffer, Lighter and Longer-Lasting Machines

Machinery is usually built in small numbers, or even as a one-off, so there is rarely room for a prototype that fails. Simulation helps you:

• Get it right first time: check stiffness, strength and vibration before ordering parts.
• Build lighter without losing stiffness: remove material where it does nothing and add it where it counts.
• Run faster: stiffer, lighter moving parts settle quicker and allow higher speeds and accelerations.
• Last longer: predict fatigue at welds, bolts and joints for the duty cycle the machine will really see.
• Fix problems in the field: find the root cause of a crack or a vibration and prove the fix before the next shutdown.

For precision machinery, stiffness often matters more than strength. A part can be far from breaking and still bend enough to ruin accuracy.

• FEA shows how much an arm, gantry or frame deflects under payload, process forces and its own weight, and where that deflection comes from.
• For robots, the loads come from motion as well as weight: the accelerations at each joint can be taken from motion studies and applied to the structure.
• Checking the structure in several arm positions reveals the worst-case pose.

We took this approach in our structural strength analysis of a 6-DOF robotic drilling arm and its joints, where the complete arm and its bolted joints were checked under drilling loads. The same checks apply to the structures that support a machine, as in our FEA of a beam bracket for structural integrity.

Every structure has natural frequencies. If a motor, a spindle, a gear mesh or the robot's own motion excites one of them, the machine resonates.

• Modal analysis finds the natural frequencies and mode shapes, so they can be kept clear of operating speeds.
• Harmonic and transient analysis show how large the vibration gets and how long a robot or gantry takes to settle after a move, which limits cycle time.
• For machine tools, a stiffer, better-damped structure reduces chatter and improves surface finish.

Once the mode shape is known, the fix is often simple: a rib in the right place, a stiffer mount or a different support layout.

Machines run for millions of cycles, so most structural failures are fatigue failures, and they usually start at welds, holes and sharp corners.

• FEA finds the stress concentrations and the stress range at each hot spot for the machine's real duty cycle.
• Welds are assessed with established methods, such as the IIW recommendations or the detail categories of EN 1993-1-9 (Eurocode 3), to predict fatigue life.
• Small changes, like moving a weld away from a high-stress area or adding a generous radius, can extend fatigue life many times over, because life is very sensitive to the stress range.

Bolted joints hold machines together, and they can fail in ways a simple hand calculation misses: loss of preload, joint slip, gapping between plates or bolt fatigue.

• FEA with contact models the bolt preload, the clamped parts and the external loads together, showing whether the joint stays closed and how much load the bolts really carry.
• Results can be checked against VDI 2230, the widely used guideline for highly stressed bolted joints.
• Robot joints, motor mounts, gearbox flanges and base plates all benefit from this check.

We used the same preload-then-load approach in our FEA of a bolted flange joint under bolt preload and pressure.

In moving machinery every kilogram costs: heavier arms and carriages need bigger motors and gearboxes, accelerate more slowly and use more energy.

• Topology optimisation shows where material is really needed for a given set of loads, as a starting point for a lighter design.
• Material comparisons, such as steel against aluminium or composite, show the trade-off between weight, stiffness and cost.
• Lighter moving parts allow faster cycle times with the same motors, or smaller motors for the same speed.

A fixture that flexes under clamping or cutting forces moves the part, and the error ends up in every part it holds.

• FEA checks fixture deflection under clamping and machining loads, so the part stays where it should.
• It shows whether clamping forces distort thin-walled parts.
• Material can be taken out of over-designed fixtures to make them lighter and easier to handle.

Our FEA and optimisation of an industrial fixture in SolidWorks Simulation is an example of this kind of study.

Heat is the enemy of accuracy and reliability. It limits motor and drive performance, and thermal growth moves spindles, axes and tool tips.

• Electromagnetic FEA predicts torque, magnetic flux and losses in electric machines, as in our electromagnetic FEA of a synchronous machine in Ansys Maxwell.
• CFD of the cooling air or liquid keeps motors, drives and control cabinets within their temperature limits; see our CFD study of a duct designed to improve cooling.
• Thermal FEA predicts temperature rise and thermal growth, from machine structures to processes such as laser heating, as in our transient thermal analysis of a laser heat source on a plate.

Machine guards and robot cells must contain broken tools, ejected parts and collisions.

• Explicit dynamics, the method we used in our impact simulation in Ansys Explicit Dynamics, shows whether a guard panel stops an ejected part and how a structure deforms in a collision.
• Guards are designed to standards such as ISO 14120, and industrial robots and robot cells to ISO 10218. Simulation helps you reach a design that meets them before testing.

To give you an accurate quote and get started quickly, send us as much of the following as you have:

• 3D CAD files (STEP, IGES, Parasolid or native files), or drawings for our 3D CAD team to model.
• Materials, including weld details and bolt sizes and grades.
• Loads and duty cycle: payloads, process forces, speeds, accelerations and the number of cycles.
• The motion profile for robots and moving axes, if you have it.
• Any standards or customer requirements the machine has to meet.
• Test data, photos of failures or vibration measurements, if the machine already exists.